Dynamic multiplier circuit



April 1935- J. HIHAMMOND, JR 1 ,998,618

DYNAMIC MULTIPL'IIER CIRCUIT Original Filed Nov. 1, 1950 OUTPUT A TTORNEYS Patented Apr. 23, 1935 UNITED STATES PATENT OFFICE DYNAMIC MULTIPLIER CIRCUIT Application November 1, 1930, Serial No. 492,661 Renewed September 28, 1933 13 Claims.

This invention relates to amplifying systems and more particularly to an improved system for controlling the amount of amplification in accordance with the strength of the applied energy.

The invention relates particularly to a system of amplification in which a greater ratio of amplification or gain is produced for impressed signals of high intensity than for impressed signals of low intensity.

The invention provides means for varying the impedance external to a space discharge ampliher by changing the impedance of a control device associated therewith, thus causing the ampliflcation of the system to vary in accordance with the input signal strength.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in which The single figure illustrates diagrammatically the system as applied to the reproduction of the sound record of a talking moving picture pro jector or of a phonograph.

In the following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

Referring more particularly to the accompanying drawing, a source of illumination III is provided, the light from which is focused, by means of a lens ll, through an aperture l2 in an aperture plate It, and upon the sound record of a moving film it. The light which passes through this film is focused by means of a lens I5 upon a photoelectric cell i6. This cell is connected through a transformer i1 to one side of a doublepole double-throw switch I8, the other side of which is connected to a phonograph pick up ID.

The blades of the switch iii are connected through a transformer 2| to the input circuits of two space discharge tubes 22 and 23 which are connected in parallel to a common filament battery 24 and a common biasing battery 25. The output circuit of the space discharge tube 22 (which may be called the amplifier tube) includes a plate battery 26, and the primary of a transformer 21, the secondary of which is connected to the input circuit of a push-pull amplifier 28. The output circuit of this amplifier 28 is connected through a transformer 29 to the moving coil of a loud speaker 3|. 'lhe field winding 32 of this loud speaker is supplied with current from a battery 33.

The output circuit of the space discharge tube 28 (which may be called the first control tube) includes a plate battery 35 and a resistance 36 which is shunted by a condenser 31. of the resistance 36 is connected to the input circuit of a third space discharge tube 38 (which may be called the second control tube), the output circuit of which is connected in parallel with the output circuit of the space discharge tube 22. The filament of the space discharge tube 38 is also heated by the battery 24.

In the operation of the form of the invention shown in the accompanying figure, when it is desired to use the photoelectric pick up, the switch It! is thrown to the upper position, and. when it is desired to use the phonograph pick up, this switch is thrown to the lower position.

In either case, the energy received passes through the transformer 2| to the input circuits of the space discharge tubes 22 and 23. The amplified output from the amplifier tube 22 passes through the primary of the transformer 21 and the space discharge tube 88. The energy from the secondary of the transformer 21 passes to the push-pull amplifier 28 where it is further amplified. The output from this device 28 then passes through the transformer 29 to the moving coil of the loud speaker 3! where it is reproduced as speech or music in the usual manner.

Part of the input energy passes to the first control tube 28 which acts as a detector causing current to flow in the direction of the arrow through the resistance 38, thus building up a potential difference across it which isproportional to this current and, therefore, proportional to the input signal strength.

With low intensity input signal the negative potential applied to the grid of the second control tube 38 due to the current in the resistance 36 is small, thus causing the impedance of the second control tube 38 to be small which in turn allows a large current to flow through this device. In this way a considerable proportion of the out= put of the amplifier tube 22 passes through the second control tube 38, thus reducing the amount of energy passing through the transformer 2? which cuts down the output of the loud speaker One side Y shown herein, it is to be understood that the 3|. In this way the amplification ratio of the system is decreased.

With increase of signal strength, more current will flow through the resistance 36, thus increasing the negative potential applied to the grid of the second control tube 38 which causes an increase of its impedance, thus reducing the current flowing through it. This causes less of the output of the amplifier tube 22 to be shunted through the second control tube 38, and therefore, a greater proportion will pass through the transformer 21 to cause an increase of volume in the loud speaker 3|. In this way the amplification ratio of the system is increased.

It is thus seen that, with low input signal strength, the amplification ratio of the system will be low due to a decrease in the impedance external to the amplifier, thus causing a large proportion of the output energy of the amplifier to beby-passed through the device 38. With high input signal strength the amplification ratio of the system will be high due to an increase of the external impedance which allows only-a small proportion of the output energy to be by-passed.

Although only a few of the various forms in which this invention may be embodied have been invention is not limited to any specific construction, but might be embodied in various forms without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

1. In a system for reproducing sound from a record, a space discharge device, a second space discharge device in parallel therewith, a resistance in the plate circuit of said second device, a third space discharge device, said resistance being also in the input circuit of said third space discharge device, the output circuit of said third device being in parallel with the output circuit of said first device.

2. In a system for reproducing sound from a record, a space discharge device, a second space discharge device having an output circuit, said output circuit forming a shunt path for the output of said first device, a third space discharge device having an input circuit said input circuit being in parallel with the input circuit of said first device, a resistance in the output circuit of said third device said resistance also being in the input circuit of said seconddevice.

3. In a system for reproducing sound from a record, an electron discharge device having an output circuit, a second electron discharge device also having an output circuit, both of said output circuits being connected in parallel, a third electron discharge device having an input circuit which is in parallel with the input circuit of said first device, a resistance in the output circuit of said third device which is also in the input circuit of said second device and means for varying the current in said resistance in accordance with the input signal strength, thus varying the impedance of the second device which varies the amplification ratio of the first device.

4. In a system for reproducing sound from record, an electron discharge device having a control element, a source of signal, means for impressing said signal on said control element, a second electron discharge device having a control element, means for impressing said signal on the control element of said second device, a resistance in the path of the space current of said second electron discharge device, a third electron discharge device having a control element, said resistance being so arranged that the voltage drop therein caused by the space current of the second electron discharge device controls the potential applied to the control element of the third electron discharge device and means for varying the external impedance of said first device by the change of impedance of said third device due to the variation of potential applied to the control element thereof.

5. In a system for reproducing sound from a record, an electron discharge device having a control element, a source of signal, means for impressing said signal on said control element, a second electron discharge device having a control element, means for impressing said signal on said second device, a resistance in the path of the space current of said second electron discharge device, a third electron discharge device having a control element said resistance being so arranged that the voltage drop therein caused by said space current controls the potential applied to the control element of said third electron .discharge device, thus varying the impedance of said third device which causes a variation of the amount of energy shunted from the output circuit of said first device thus controlling the amplification ratio of said first device so that it is greater for strong signals than for weak ones.

6. In a system for reproducing sound from a record, an amplifier tube, first and second control tubes, each tube having an anode, a cathode and a control electrode, means for impressing a signal on the cathode-control electrode circuits of said amplifier tubeand said first control tube, a first source of B-voltage and a resistance in the anode-cathode circuit of said first control tube, a capacitance across said resistance, said resistance being in the control electrode-cathode circuit of said second control tube, a second source of B-voltage and an output device in the anodecathode circuit of both said second control tube and amplifier tube.

'7. In a system for reproducing sound, a sound record, a pick-up device therefor, a space discharge amplifier fed by said pick-up device and means for varying the average external impedance of said amplifier in accordance with the average strength of the signals fed to said amplifier, thus varying the amplification ratio of said amplifier for strong and weak signals.

8. In a system for reproducing sound, a sound record having moderate contrast between loud and soft notes, a pick-up device therefor, a space discharge amplifier having an input circuit fed by said pick-up device and also having an output circuit, a variable impedance device shunted across said output circuit and means controlled by the average strength of the signal impressed on said input circuit for determining the average impedance of said impedance device, thus varying the amplification ratio of said amplifier so that it is greater for strong signals than for weak signals,

9. In a system for reproducing sound, a sound record having a moderate volume ratio between 1,998,618 amplifier, thus varying the amplification ratio of said first amplifier so that it is greater for strong signals than for weak signals.

10. The method of operating a space discharge amplifier in the reproduction of sound from a sound record which comprises varying the average external impedance of said amplifier in accordance with the average strength of the signals fed to said amplifier, thus varying the gain ratio of said amplifier for strong and weak signals.

11. In a system for reproducing sound, a sound record having moderate contrast between loud and soft notes, a pick-up device therefor, a space discharge amplifier having an input circuit fed by said pick-up device and also having an output circuit, a variable impedance device adapted to vary the impedance of said output circuit, and means controlled by the average strength of the signal impressed on said input circuit for determining the average impedance of said impedance device.

12. The method of operating a space discharge amplifier in the reproduction of sound from a sound record which comprises amplifying the sound energy received from said record in said amplifier while varying the external impedance of said amplifier in accordance with the strength of the input signal so as to expand the volume ratio of the output of. the amplifier with respect to the input thereof.

13. The method of reproducing sound from a sound record which comprises picking up the en ergy variations of said record, applying said variations to a space discharge amplifier, varying the external impedance of said amplifier in accordance with the strength of said energy variations, and applying theoutput of said amplifier to a translating device.

JOHN HAYS HAMMOND, JR. 

